There is a proposal on a reflective type liquid crystal display device having a parallel alignment type liquid crystal layer as optical modulation means (e.g., see Patent Document 1).
[Patent Document 1] Japanese Patent Application Laid-Open No. 249126/99 (e.g., paragraphs [0007] to [0013])
The liquid crystal optical element disclosed in this publication is comprised of a parallel alignment type liquid crystal layer, a polarizing plate and a mirror electrode disposed on the front and back sides thereof, respectively, and two kinds of phase difference plates interposed between the parallel alignment type liquid crystal layer and the polarizing plate, and is intended to obtain a bright and high contrast display over a wide viewing angle range in the element and to optimize retardation values of the phase difference plate and the liquid crystal layer.
However, such optimization is also applicable to a structure using a HAN (hybrid aligned nematic) type liquid crystal layer and bend alignment type liquid crystal layer, and so it is not specialized for the structure using a parallel alignment type liquid crystal layer and it is hard to say that it fully exploits advantages of the parallel alignment type liquid crystal layer.
The present inventor has noted that in a parallel alignment type or homogeneous alignment type (hereinafter these will be referred to as ‘parallel alignment type’) liquid crystal layer, all liquid crystal molecules are basically arranged parallel with upper and lower substrate surfaces sandwiching the liquid crystal layer and in the same direction under a predetermined reference electric field (e.g., no electric field), or in other words the direction of a director of the liquid crystal molecules is substantially parallel with the substrate surface, and therefore it is possible to recognize an average tilt angle of the liquid crystal molecules more accurately and easily than ones of other types. Furthermore, the present inventor has also noted that the parallel alignment type liquid crystal layer does not require additional conditions for alignment control such as a bias voltage which is required for a bend alignment type liquid crystal layer, for example and can adopt a relatively easy alignment control mode. Then, from these viewpoints, the present inventor has come to recognize that just the optimization way specific to the parallel alignment type which exploits such advantages of the parallel alignment type allows a display device using the parallel alignment type liquid crystal layer to obtain a desired viewing angle characteristic most effectively.
Furthermore, while it is desired to take measures for obtaining a desired viewing angle characteristic through an approach different from those described in the above-mentioned Patent Document, there is also an expectation of such optimization in the case where a parallel alignment type liquid crystal layer is applied to a liquid crystal display device other than the reflective type one, such as a recently practically-used, so-called Transflective type liquid crystal display device.